fix: ModuleNotFound on run cmd

[antazoey]

What I did

Tried running silverback run in a random directory to see what happens. Got ModuleNotFounder error which I thought was kind of strange. I attempted to improve the experience there.

How I did it

Another try and except and this time raise click.BadParameter

How to verify it

Go to a random directory with no bots.
Run silverback run

Should see:

Usage: silverback run [OPTIONS] [BOT]
Try 'silverback run --help' for help.

Error: Invalid value for '[BOT]': Nothing ro run: No bot argument(s) given and no bots module found.

Is much better than it was.

Checklist

• Passes all linting checks (pre-commit and CI jobs)
• New test cases have been added and are passing
• Documentation has been updated
• PR title follows Conventional Commit standard (will be automatically included in the changelog)